Java信号量是否使用忙等待或默认等待/通知？

Question

As the question goes. I'm using the JDK 6.0 on Windows 7, and am attempting to use semaphores as a mechanism to solve a synchronization problem. It works perfectly, but I'm trying to avoid busy waiting in my problem.

I would just ask the java documentation and spare SO the trouble, but the docs go like this:

Acquires the given number of permits from this semaphore,
 blocking until all are available, or the thread is interrupted.

Acquires the given number of permits, if they are available,
 and returns immediately, reducing the number of available permits
 by the given amount.

If insufficient permits are available then the current thread
 becomes disabled for thread scheduling purposes and lies dormant

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/Semaphore.html#acquire(int )

That is to say, the docs seem to be implying both answers. Which one is correct?

Answer 1

I don't see how it's implying busy-waiting at all. It clearly states that the thread is "disabled" and dormant. Basically, it's cheap: the thread won't consume processor time while it's waiting to acquire the semaphore.

Answer 2

It's clearly wait/notify due to this line:

If insufficient permits are available then the current thread becomes disabled for thread scheduling purposes and lies dormant.

This means the thread is not scheduled by the OS until the event to wake it up (available semaphore permits) occurs, at which point the thread is signaled to continue execution.